GOCE - Re-Entry UpdatesRe-Entry Updates will be posted on this site. For more on the GOCE spacecraft, its mission and science, scroll down below the Re-Entry Section.

Final GOCE Re-Entry Round-Up - A Look at the Data

November 11, 2013

ESA’s GOCE satellite re-entered the atmosphere early on Monday morning, UTC following the completion of its science mission dedicated to mapping the Earth’s gravitational field. Re-Entry took place around 0:16 UTC over the South Atlantic Ocean, near the Falkland Islands.

GOCE, the Gravity Field and Steady-State Ocean Circulation Explorer, was delivered to orbit atop a Rockot launcher blasting off on March 17, 2009 from the Plesetsk Cosmodrome, Russia. Since then, GOCE used a high-fidelity payload consisting of a Electrostatic Gravity Gradiometer to precisely measure the gravity field of the Earth with unprecedented accuracy. GOCE set out to create a high resolution map of Earth's gravity field with special focus on local phenomena and gravity anomalies. For that, the spacecraft needed to be operated at a very low orbital altitude of under 270 Kilometers which, late in the mission, was lowered further to 224 Kilometers. At that altitude, the thin atmosphere of Earth causes noticeable drag on the spacecraft - requiring the vehicle to constantly maintain its orbit using a propulsion system featuring a small ion engine that ejected Xenon ions at high velocities to compensate for orbital decay.

Image: ESA/AOES Medialab

Re-Entry Observation from the Falkland Islands

We saw it burn up from the Falklands at about 9.20pm last night. Came from the South breaking up into bits. pic.twitter.com/54DwAiTI0k

After more than four years of operation, the Xenon supply of GOCE ran out on October 21. No longer flying in Drag-Free-Mode, GOCE immediately started to lose altitude as drag caused the satellite to slow down. In late October, re-entry models predicted GOCE to re-enter around mid-month in November, but accurate estimates were not possible this far out as solar activity is the major driver of conditions in the upper atmosphere.

Orbit Evolution over the entire GOCE Mission

Plot: Heavens-Above.com

As the sun picked up the pace, sending a number of flares into Earth’s direction, the atmosphere expanded which increased drag levels on GOCE. About one week ahead of entry, predictions shifted to November 11 & from then on only showed small drifts between the late hours on the 10th and the early hours of the 11th.

One of the unique aspects of the GOCE re-entry was that the satellite was still active and functional as it approached orbital decay. Most spacecraft that enter the Earth’s atmosphere are dead long before orbital decay, but GOCE continued to fly in a controlled fashion. The spacecraft functioned exceptionally well – its attitude control system remained in fine-pointing mode and its Gradiometer continued to provide valuable data and the Satellite-to-Satellite tracking system was up and running as well. Measurements that were made over the final days of the mission can be used to study atmospheric density and winds at altitudes that no operational satellite could reach.

Also, having a satellite operational until re-entry provides insight into the environment just before orbital decay – looking at how the spacecraft responds to being in an extreme environment it was never designed to work in.

Starting on November 9, drag on the satellite increased rapidly reaching levels of 90 millinewtons causing saturation events on the accelerometers of the vehicle. During the nominal mission of GOCE, drag was on the order of 2 and 4 millinewtons with peaks close to 8mN. By Sunday, drag was so high that no useful Gradiometer data could be acquired any longer, so teams switched the instrument off. However, the GPS systems and other telemetry systems of the vehicle were still in good condition.

Over the course of the day on Sunday, ESA kept in touch with the spacecraft via the Kiruna ground station in Sweden and the Troll Station, Antarctica. During regular Comm Passes, GOCE downlinked telemetry data which showed that it was getting uncomfortable for GOCE as computer and battery temperatures started climbing. By 18:00 UTC, GOCE was well below 130 Kilometers.

A look at the Data

ESA and USSTRATCOM were tracking the satellite closely to provide re-entry predictions. GOCE made its final ground station pass at 22:42 UTC and orbital data from that pass was used by ESA to propagate the orbit and determine an approximate re-entry location. This prediction saw GOCE re-entering on the descending node of its orbit, passing over Siberia, Asia and the Indian Ocean & skimming the coast of Australia. ESA’s Entry Window was centered on 23:50 UTC with a margin of one hour to each side of that point in time.

USSTRATCOM provided a prediction at 21:40 UTC that was in good agreement with ESA’s assessment, putting re-entry at 23:58 UTC, plus/minus one hour, also on the descending node.

The final orbital elements issued for GOCE had an epoch of 23:02 UTC.

Image: TLE Analyser/Google Earth

Using those Two Line Elements and the orbit propagation software SatEvo provided us with a predicted decay time of 0:09 UTC – right on the point where GOCE transitioned from its descending node to its ascending node.

But after all those years flying in the thin atmosphere, GOCE would not give up that easy, keeping on flying and starting another ascending pass.

After re-entry, USSTRATCOM provided the precise time and location of the orbital decay of the GOCE satellite. GOCE re-entered at 0:16 UTC on Monday, November 11, 2013 after 1,700 days in orbit. This re-entry time can be given with an accuracy of +/-1 minute since USSTRATCOM has access to space and ground-based surveillance assets to pin-point the location of entry. The time given for orbital decay represents the time of GOCE passing the 80-Kilometer mark.

At that point, GOCE was at a position of 60° West 56° South – above the South Pacific Ocean about 360 Kilometers from the south-eastern tip of South-America and 410km south of the Falkland Islands.

As the spacecraft re-entered, heat started building on the vehicle and aerodynamic forces occurring at the high entry velocity caused the satellite to break up. Most components of the disintegrating spacecraft were expected to burn up harmlessly in the atmosphere and never reach the ground, but it is known that about 20 to 40% of a re-entering satellite's total mass reach Earth's surface. Dense components of satellites usually impact 800 to 1,300 Kilometers downrange from the Orbital Decay Point. Their journey back to Earth is strongly influenced by atmospheric properties like crosswinds that play a major role during atmospheric descent.

As GOCE was starting its ascending node when re-entry occurred, it was still more than 1,500 Kilometers from making landfall over Argentina. With high probability, surviving fragments of the satellite fell into the South Atlantic Ocean and did not reach land.

The re-entry event was visible from Tierra del Fuego and the Falkland Islands. Sightings from the Falklands were reported via Twitter.

Coming to a close with satellite pieces resting in peace at the bottom of the Ocean, the GOCE mission has returned unprecedented scientific results and more is yet to come as science data from its recent low-altitude mission is examined.

Latest Update

Post-Re-Entry Report (November 11, 2013 - 4 UTC)

USSTRATCOM Re-Entry Estimation: November 11, 2013 - 00:16 UTC +/-1 MinuteOrbital Decay at the center of the Re-Entry Window places the point of Orbital Decay at the following location in the ascending node of the orbit:60° West 56° South - 360 Kilometers from the south-eastern tip of South America - 410 Kilometers south of the Falkland Islands

Re-Entry Orbit

Image: Orbitron

Estimated Decay Location

Image: TLE Analyser/Google Earth

November 11, 2013:[01:45 UTC]: ESA has confirmed that the GOCE Satellite has re-entered the atmosphere. Location and time are still unclear.[00:50 UTC]: The re-entry window is now closed. With very high certainty, GOCE has re-entered by now. Pin-pointing the decay location and exact time is a process that requires some time.November 10, 2013:[23:50 UTC]: Approaching the predicted re-entry time. If it has not already entered the atmosphere, GOCE should decay in the next few minutes.[23:40 UTC]: No more GOCE Communication Passes are expected from this point on. Pin-pointing a re-entry time and location may take some time unless visual observations are reported.[23:03 UTC]: GOCE Elset Epoch. Orbit: 109 by 121 Kilometers - SatEvo computes decay at 0:09 UTC on November 11[22:50 UTC]: Re-Entry Window Open! GOCE is likely to re-enter on the descending node of its upcoming orbit that takes it over the Pacific Ocean, parts of Asia and the Indian Ocean. See map below.[22:42 UTC]: GOCE still alive! Expected Comm Session with Troll Ground Station. Signal acquisition nominal, telemetry nominal. Computer Temp is 80°C, battery is at 84°C. Crossing the 120-Kilometer mark.[22:30 UTC]: Propagating the latest orbital data provides an orbit of 118 by 127 Kilometers

[18:56
UTC]: Expected Communications session of GOCE with the Kiruna Ground
Station. Acquisition of Signal was nominal. GOCE still operating[18:15 UTC]: New Re-Entry Prediction: November 11, 2013 - 00:03 UTC +/-5 Hours, Map Updated[17:46
UTC]: ESA reports that GOCE is below 130 Kilometers in altitude. The
Kiruna Ground Station completed a successful comm pass at 17:30 UTC and
GOCE is still maintaining its attitude. Battery and computer
temperatures are rising, now at ~45°C.[15:47 UTC]: GOCE is still tracked in orbit. 131 by 142 Kilometers.[15:30
UTC]: GOCE is now at 133 Kilometers dropping about 1.5km per hour and
re-entry is less than 10 hours away. The satellite is still operating.
Drag levels are preventing any more Gradiometer science so the
instrument was switched off. GOCE is in a stable attitude, continuing to
make good measurements with its GPS receivers. ESA plans to operate
the satellite as long as possible, keeping up regular ground station
passes to downlink data.[14:15 UTC]: GOCE expected to re-enter before the end of the day, UTC - Calculated orbit: 137 by 145 km

ESA's GOCE Satellite is approaching the end of its mission in Low Earth Orbit - eventually headed for destructive re-entry after running out of Xenon that was used for its electric propulsion system. GOCE, the Gravity Field and Steady-State Ocean Circulation Explorer, was delivered to orbit atop a Rockot launcher blasting off on March 17, 2009 from the Plesetsk Cosmodrome, Russia.

Since then, GOCE used a high-fidelity payload consisting of a Electrostatic Gravity Gradiometer to precisely measure the gravity field of the Earth with unprecedented accuracy. GOCE set out to create a high resolution map of Earth's gravity field with special focus on local phenomena and gravity anomalies. For that, the spacecraft needed to be operated at a very low orbital altitude of under 270 Kilometers. At that altitude, the thin atmosphere of Earth causes noticeable drag on the spacecraft - requiring the vehicle to constantly maintain its orbit using a propulsion system.

Image: ESA

The aerodynamically shaped GOCE satellite carries an ion propulsion system that ejects Xenon ions at high velocities to compensate for orbital decay. Now, after more than four years in orbit, the Xenon has run out.Without propulsion, GOCE can no longer maintain its orbit and is expected to decay within two or three weeks. The propulsion system stopped working on October 21 - setting the stage for the re-entry of the 1,100-Kilogram satellite over any point under its ground track.

The Entry Process

GOCE is a relatively large object to re-enter Earth's atmosphere - having a mass of just under 1,100 Kilograms with a spacecraft length of 5.3 meters. Another important factor to consider in this particular case is the aerodynamic shape of the satellite that will allow it to enter a more stable position during entry instead of the typical tumble most spacecraft exhibit during their final days in orbit. Once GOCE runs out of Xenon, the satellite will gradually lose orbital altitude as it is slowed down as a result of drag in the upper atmosphere. Even at altitudes of more than 200 Kilometers, the thin atmosphere consists of atoms and molecules that collide with the spacecraft and slow it down as a result. Over a period of about two weeks, GOCE will slowly lose altitude, starting with a slow decay that will accelerate quickly when the vehicle dips inside 200 Kilometers. The exact speed of the orbital decay depends on the current state of the atmosphere which is known to expand and contract as a result of solar activity. Once hitting the dense atmosphere, GOCE will start feeling the effects of re-entry. The precise altitude of the start of re-entry depends on atmospheric conditions.

Usually, destructive re-entry starts at an altitude of 120 to 100 Kilometers as the spacecraft is rapidly slowed down and dips into the dense layers of the atmosphere. Once the Spacecraft hits the dense atmosphere, friction will cause it to heat up and aerodynamic forces occurring at these high velocities lead to the break-up and disintegration of the vehicle.

With its fins and aerodynamic shape, GOCE will maintain a stable position in orbit as it approaches entry. During entry, the spacecraft will likely remain in that position for the initial phase of re-entry until it breaks up. Following the destruction of the spacecraft, most of its components will harmlessly burn up in the atmosphere.

Photo: NASA

However, it is known that about 20 to 40% of a re-entering satellite's total mass reach Earth's surface. Dense components of satellites usually impact 800 to 1,300 Kilometers downrange from the Orbital Decay Point. Their journey back to Earth is strongly influenced by atmospheric properties like crosswinds that play a major role during atmospheric descent.

Forecasting the time and location of orbital decay is difficult as it depends on a number of variable factors that have to be taken into account. First estimates will become available several days ahead of Re-Entry, but those will have a large margin for error, making it hard to pin-point the exact location.

About one day before entry, zones over which the satellite will not re-enter can be determined as the re-entry window shrinks to just a few orbits. Predictions will become more fine-tuned over the final two hours of the spacecraft’s life.

GOCE is orbiting Earth in a polar orbit with an inclination of 96.7 degrees which means that the spacecraft could decay above virtually any location on Earth.

Witnessing Re-Entry

As described above, predicting the exact timing of re-entry is nearly impossible, but the re-entry window that is issued based on orbital tracking can help when trying to watch the event. The exact location of re-entry can not be predicted, however a few hours before the event, zones will be excluded. Should you have visible passes around the time of final entry predictions that are made on the day of the estimated Re-Entry, you should certainly step outside and look for the spacecraft. Websites like Heavens-Above.com provide a list of passes for any given location on Earth. (Pass Predictions of these websites are based on orbital information that is updated several times per day. On Re-Entry day, the spacecraft's orbit decays rapidly so that these predictions become inaccurate very fast and the time of the start of the pass might vary by several minutes.) In the days leading up to re-entry, GOCE can be seen as a little dot racing across the sky. When re-entering, the disintegrating vehicle will streak across the sky with a visible plasma tail and glowing debris falling back to Earth.

GOCE Spacecraft & Instrument Overview

The 1,060-Kilogram GOCE Spacecraft, built by Thales Alenia Space, is 5.3 meters long and features an aerodynamic design to reduce drag on the vehicle when orbiting the Earth at particularly low altitudes. GOCE has a small cross section to limit drag on the vehicle.

The satellite's body has the shape of an octagonal prism featuring fins for stabilization. GOCE has been fabricated with carbon-fiber reinforced plastic components that also carry all structural loads. The satellite is divided into seven compartments that house the different equipment. GOCE is symmetrical in shape to avoid disturbances and uses materials with high thermo-elastic stability to provide a very stable environment to its sensitive instrument. Orbiting in a sun-synchronous orbit at a constant vehicle attitude allowed engineers to mount solar panels on the satellite's hot side that is illuminated by the sun and install radiators on the cold side that is in permanent shadow to keep the satellite's systems at a constant temperature. Onboard batteries (78Ah) and avionics are used for power storage and distribution as part of a 24-32-Volt unregulated main power bus. The solar panels provide 1,300 Watts of power.

Image: ESA

GOCE uses star trackers for navigation and magnetic torquers for attitude control and angular acceleration control. Magnetometers and coarse sun sensors are used for attitude acquisition in safe mode. Thermal control is accomplished passively with insulation material and actively with a number of heaters on the vehicle. Excess heat is dissipated using radiators.

Image: ESA

Data acquired by the instruments and collected telemetry is stored in a 2 x 4 Gbit mass memory. GOCE uses a 1553 main data bus and a 32-bit RISC single chip processor for data handling. The spacecraft is equipped with a redundant system of two S-Band transmitters for communications. S-Band is used for telemetry and data downlink, command uplink and ranging for precise orbit determination. Downlink data rates of 1.21Mbit/s are achieved while command uplink is limited to 4kbit/s. The two hemispherical S-Band antennas are installed on the solar array edges.

To maintain its low orbital altitude and prevent the spacecraft from re-entering, GOCE uses an ion propulsion system built by QinetiQ. The thrusters generate Xenon ions and accelerate them to a velocity of more than 40,000 meters per second at which they are ejected to push the spacecraft forward. The thrusters are operated in closed loop mode being controlled by the onboard computer that processes gradiometer common-mode acceleration measurements. The thrusters can be operated at different thrust levels as low a 1 millinewton and up to 22 millinewtons.

This Drag-Free and Attitude Control System uses data provided by the three star trackers, two digital sun sensors, a coarse Earth and sun sensor, a three-axis magnetometer and Gradiometer data as well as satellite-to-satellite tracking via GPS. This data is processed in real time to accurately determine spacecraft orientation, position and accelerations. The two ion thruster assemblies are used for drag-free orbit control to precisely maintain semi-major axis while the magnetic torquers are used for attitude control.

A cold-gas thruster assembly known as the Gradiometer Calibration Device was used to shake the satellite for Gradiometer calibrations. GOCE can operate in Coarse Pointing Mode, Fine Pointing Mode and Drag-Free mode which is the science mode during which the thrusters are operated to perfectly maintain the vehicle's orbit.

Depending on solar activity, the propulsion system was operated at thrust levels between 2 and 4 millinewtons with peaks close to 8mN during increased solar activity and drag. The drag-free control system has worked very well throughout the mission, allowing GOCE to acquire high-quality data with its science instruments

Image: ESA

GOCE is equipped with a highly sensitive Electrostatic Gravity Gradiometer, EGG, that measures the all components of the Gravity Gradient Tensor. The instrument is based on an ambient temperature, closed loop, capacitive accelerometer design consisting of three pairs of three-axis servo-controlled capacitive accelerometers on an ultra-stable carbon-carbon structure. The instrument is installed in close proximity to the spacecraft Center of Mass to allow it to make its high resolution measurements. The EGG measures accelerations on all axes with an accuracy of 10^-12 m/s². Even tiny accelerations as a result of Earth's gravity field can be detected in order to reveal any irregularities.

GOCE determines its precise position using a 12-channel GPS receiver that is the heart of the Satellite-to-Satellite Tracking Instrument.

EGG System

Image: ESA/ONERA

Core Gradiometer

Image: TAS/ONERA

Satellite-to-Satellite GPS Tracking

Image: ESA

GOCE Mission

Photo: ESA

GOCE was launched atop a Rockot launch vehicle on March 17, 2009 making a thundering blastoff from the Plesetsk Cosmodrome in Russia. The two stages of the Rockot delivered the Briz-KM upper stage and GOCE satellite to a sub-orbital trajectory from where the upper stage boosted the stack into orbit followed by a circularization burn during the first orbit before GOCE was released into a 283-Kilometer orbit at an inclination of 96.7 degrees. After completing its initial steps in orbit - stable attitude acquisition and the initiation of communications with ground stations - GOCE entered a three-day Early Operations Phase to configure the spacecraft for commissioning that took about 7 months to complete. During on-orbit commissioning, GOCE started to operate its propulsion system, the navigation systems and the Gradiometer.

While commissioning was in progress, the orbit slowly decayed to 254 Kilometers at which point the Drag-Free Mode was initiated. After extensive calibrations of the Gradiometer, the GOCE spacecraft entered routine science operations - measuring Earth's gravity field with unprecedented accuracy in an orbit with a repeat cycle of 61 days.

In February 2010, GOCE experienced computer problems, causing an interruption in science data acquisition and Drag-Free Flight while teams configured the backup computer for use. After resuming nominal operations, GOCE again faced technical trouble in July 2010 when the spacecraft failed to downlink science data to the mission's dedicated ground station in Kiruna, Sweden. The issue was traced back to a faulty communications link between processor module and the telemetry modules of the flight computer. After two months of troubleshooting, teams found a solution - raising the temperature in the computer compartment by 7°C to allow the equipment to function properly.

In September 2010, science data acquisition in Drag-Free mode was resumed. In November 2010, the mission was extended by 18 months to collect more data. Initially, the Xenon fuel was expected to run out after a nominal mission of 20 months, but a calm sun and good propulsion system performance allowed teams to extend the mission. In 2010, the first high-resolution gravity maps produced with GOCE data were presented to the scientific community. Vehicle operations in 2011 were uneventful as the spacecraft continued to collect valuable data.

In the summer of 2012, the mission teams allowed the vehicle to drop in altitude as operating the GOCE spacecraft in lower orbits would provide data at higher quality and spatial resolution. The orbit was lowered from 254 Kilometers to 235 Kilometers. Then in May 2013, the spacecraft was placed in a 224-Kilometer orbit with a repeat cycle of 143 days - flying much lower than any other scientific satellite in Earth orbit. Over the final six months of the mission in the 224-Kilometer orbit, GOCE acquired even better data showing minute local gravity differentials. GOCE is operated by its mission team until its Xenon supply runs out.

When the propellant tank is empty, teams will continue to operate the vehicle to gather science data until the last possible moment as the reduced altitude just before entry presents the opportunity of gathering even better data. Data acquisition and orbit determination will continue as long as the satellite can be operated. When drag increases, teams will passivate the spacecraft, sending it on its final days in orbit before destructive re-entry.

ESOC Space Debris Office and members of the Inter-Agency Space Debris Coordination Committee will monitor the vehicle's decay and re-entry to study space debris and orbital decay properties.

GOCE Science Accomplishments

GOCE has provided unprecedented measurements of Earth's gravity field allowing scientists to model the geoid with extremely high precision. The geoid is a surface of equal gravitational potential that is defined by Earth's gravity field and its irregularities only - with a hypothetical Ocean surface at rest without any tides. The geoid illustrates how Earth would look if its shape were distorted to make gravity the same at all places on its surface - zones of intense gravity are sticking out while areas of reduced gravity appear as depressions.

GOCE Geoid

Image: ESA/HPF/DLR

The gravity model and refined geoid provide better understanding of the physics of Earth's interior as well as lithosphere dynamics, mantle composition and processes such as uplift and subduction. The geoid is used to make precise calculations of ocean currents, heat transport, sea-level changes and ice dynamics which are important factors affected by climate change. GOCE was able to measure ocean flow patterns in remarkable detail that was better than expected. Additionally, the geoid is used a the reference from which to map topographical features of Earth.

GOCE set out to provide a gravity map with a spatial resolution of 100 Kilometers and determine the geoid with an accuracy of better than 2 centimeters. GOCE has already provided four geoid models, each more accurate than the last.

GOCE's science instruments proved to be capable of picking up even the smallest variations or displacements of the atmosphere at its altitude. This became apparent when GOCE detected sound waves from the March 11, 2011 earthquake that hit Japan. Sound or pressure waves are amplified as they pass into the thin atmosphere where GOCE was flying. Combining GOCE measurements with numerical models to examine the propagation of low frequency infrasound waves was something that had never been possible before.

In 2012, scientists released a map showing the global Mohorovičić discontinuity, the boundary between the crust and the mantle ranging from 70 Kilometers in depth in the mountains to 10 Kilometers beneath the ocean floor. This offered new clues for understanding the dynamic processes of Earth's interior that lead to an irregular subsurface density distribution. In addition, GOCE enabled scientists to study the lithosphere and plate tectonics & mantle convection.

Image: HPF

First GOCE Gravity Map

Image: TU Delft/ESA

Atmospheric Density measured y GOCE (right) and modeled (left)

GOCE also measured flow patterns and winds in the uppermost portion of the atmosphere by detecting forces that were not related to Earth's gravity. Atmospheric density measurements were also made as a function of drag experienced by the spacecraft.

Older Updates

November 9, 2013

The GOCE Satellite is approaching the 150-Kilometer mark as orbital decay is less than 1.5 days away. According to ESA, GOCE is still operating with average drag levels now above 90 Millinewtons. Gradiometer data is only usable when drag levels are less than 80mN. The satellite is still maintaining its attitude and will likely remain in an aerodynamically stable position until re-entry and disintegration. "Recently we have noticed a significant temperature increase in several areas of the spacecraft, arguably linked to GOCE encountering a more and more dense atmosphere as its orbit keeps dropping," GOCE Operations Manager Christoph Steiger said in a status update. Re-Entry is still expected to occur in the overnight hours on Sunday/Monday.

November 8, 2013

GOCE Predictions drift as Solar Activity increasesThe GOCE satellite is now rapidly losing altitude and is currently in a 167 by 174-Kilometer Orbit. The sun was active over the past days and sent solar flares in Earth's direction which increased atmospheric drag on the GOCE spacecraft, speeding up its orbital decay. Over the last 24 hours, re-entry predictions have drifted from mid-day on Monday to the overnight hours on November 10/11.According to ESA, the satellite is still operating as planned, exceeding all expectations. GOCE is still holding attitude, however saturation events on its accelerometers are increasing. Accelerometer and GPS data is still being acquired and will be used for atmospheric density studies.But even with the latest predictions, no approximate re-entry location can be given as the satellite covers virtually the entire globe within the current re-entry window. Re-Entry predictions will be refined as the event gets closer and it will be possible to narrow down an approximate location or exclude regions.

November 7, 2013

The GOCE Satellite is now in a 176 by 184-Kilometer orbit, dropping about 6 Kilometers per day as it experiences drag in the upper atmosphere. GOCE is still holding its orientation in fine-pointing mode, but the spacecraft could lose attitude control as it enters the more dense portions of the upper atmosphere which would speed up its orbital decay.

Models are still predicting GOCE to re-enter on Monday, November 11, 2013, +/-1 Day. Should GOCE start tumbling at some point, the satellite would re-enter earlier than that.

Plot: Heavens-Above.com

Re-Entry predictions will be refined as the event gets closer and it will be possible to narrow down an approximate location or exclude regions.

November 6, 2013

The GOCE Satellite is now in a 183 by 191-Kilometer orbit, dropping about 5 Kilometers per day as it experiences drag in the upper atmosphere. GOCE is still holding its orientation in fine-pointing mode, but the spacecraft could lose attitude control as it enters the more dense portions of the upper atmosphere which would speed up its orbital decay.

Models are still predicting GOCE to re-enter on Monday, November 11, 2013, +/-1 Day. Should GOCE start tumbling at some point, the satellite would re-enter earlier than that.

Plot: Heavens-Above.com

Re-Entry predictions will be refined as the event gets closer and it will be possible to narrow down an approximate location or exclude regions.Update/Epoch: November 6, 2013 (4:47 UTC)Preliminary Re-Entry Pedicition: November 11, 2013, +/-1 DayCurrent Orbit: 183 by 191 KilometersInclination: 96.544°Duration: 88.24minEccentricity: 0.00045Argument of Perigee: 249.6°Right Ascension of Ascending Node: 339.6°

November 4 ,2013

ESA’s GOCE Satellite has crossed the 200-Kilometer mark, continuing its slow drop towards Earth’s dense atmosphere. GOCE has lost approximately 30 Kilometers since electric propulsion stopped back on October 21. Currently, the satellite is dropping about 4.5 Kilometers per day.

Atmospheric drag on the satellite has been varying over the past several days, causing re-entry models to shift quite a bit as drag reached a peak to start the month and has since been decreasing again. Solar activity is the factor that drives the pace of orbital decay. Space Weather events cause a response in Earth's geomagnetic field and lead to an increase in drag in the upper atmosphere which will speed up the orbital decay of the satellite.

It is still too early to make accurate re-entry predictions. Modeling the satellite’s orbital decay with current atmospheric conditions provides a very approximate re-entry date which could shift considerably depending on actual atmospheric conditions. Over the past 24 hours, re-entry predictions drifted into 'early next week' as drag on GOCE was not as high as expected.

Plot: Heavens-Above.com

Re-Entry predictions will be refined as the event gets closer and it will be possible to narrow down an approximate location or exclude regions.

November 2, 2013

GOCE Satellite approaches 200-Kilometer Mark, Solar Activity could speed-up Orbital DecayThe decaying GOCE satellite is approaching the 200-Kilometer mark as the spacecraft continues its slow descent towards the dense atmosphere of Earth. Overall, GOCE has lost about 19 Kilometers since electric propulsion stopped on October 21. Atmospheric drag acting on the vehicle has increased to more than 15 Millinewtons - for reference, during the mission, the propulsion system had to provide about 5 to 8 Millinewtons of thrust to enable Drag-Free Flight. GOCE is still performing well and spacecraft activities are continuing nominally with the spacecraft in Fine Pointing Mode. Solar activity is the factor that drives the pace of orbital decay. Recently, the sun was relatively active and several Coronal Mass Ejections will reach Earth in the coming days. Space Weather events cause a response in Earth's geomagnetic field and lead to an increase in drag in the upper atmosphere which will speed up the orbital decay of the satellite.

Plot: Heavens-Above.com

Having GOCE flying through that dynamic region of the atmosphere that responds to space weather could provide valuable scientific data as the accelerometers aboard the spacecraft can be used to measure atmospheric density and winds at altitudes that no operational satellite could reach.

October 28, 2013

GOCE Satellite Approaching Re-Entry after Propulsion System ShutdownESA's GOCE Satellite stopped Drag-Free Flight on Monday, October 21 when its propulsion system could no longer operate as its Xenon supply ran out. Since then, the spacecraft has been steadily dropping as drag in the uppermost portion of the atmosphere slows the satellite down. Without propulsion, GOCE is now headed for re-entry, experiencing drag in the uppermost layers of the atmosphere causing the satellite to slow down and lose altitude before re-entering the atmosphere at some point in the next two weeks – depending on atmospheric conditions. A detailed outline of the re-entry process can be found below.

Plot: Heavens-Above.com

Overall, GOCE has already lost 14 Kilometers in mean altitude. The spacecraft is still being operated in Fine Pointing Mode and data acquisition is continuing.Update/Epoch: October 28, 2013Current Orbit: 212 by 217 KilometersInclination: 96.551°Duration: 88.79minEccentricity: 0.00039Argument of Perigee: 309.6°Right Ascension of Ascending Node: 330.8°

October 25, 2013

GOCE Satellite Approaching Re-Entry after Propulsion System ShutdownESA’s GOCE Satellite has started approaching orbital decay after its ion propulsion system stopped functioning early on Monday. The system was used to operate the satellite in Drag-Free Mode to maintain its low orbit at a constant altitude (more details on the propulsion system in the spacecraft section below). Last Thursday, the tank pressure dropped below 2.5 bar which was the design requirement for the electric propulsion system. Initially, the system continued to work fine, but its performance became erratic over the weekend. At 3:16 UTC on Monday, the satellite’s fault protection system switched off the system when operations could no longer be sustained. Without propulsion, GOCE is now headed for re-entry, experiencing drag in the uppermost layers of the atmosphere causing the satellite to slow down and lose altitude before re-entering the atmosphere at some point in the coming two or three weeks – depending on atmospheric conditions. A detailed outline of the re-entry process can be found below.

Plot: Heavens-Above.com

“Data acquisition and satellite operations will continue for about two more weeks until its systems stop working because of the harsh environmental conditions at such a low altitude. At this point, the satellite will be switched off, marking the end of activities for the GOCE flight control team,” ESA said in a press release. Re-Entry predictions will be issued as the event approaches.

October 18, 2013

Plot: Heavens-Above.com

On October 18, 2013, ESA reported that the fuel tank pressure aboard the GOCE Satellite has dropped below 2.5 bar. The ion propulsion system of the satellite was not designed to operate at these low pressures and could stop functioning at any time now which would mark the end of Drag-Free Flight. About 350 grams of Xenon remain in the tank that would be depleted by October 26 should the system continue to work all the way to the end, which is not expected. On October 18, GOCE was still maintaining its orbit.Current Orbit: 222 by 232 KilometersInclination: 96.554°Duration: 89.05minEccentricity: 0.00071Argument of Perigee: 18.4°Right Ascension of Ascending Node: 320.0°

October 14, 2013

Plot: Heavens-Above.com

As of October 14, 2013, GOCE was still orbiting in a stable orbit that the spacecraft is maintaining using its propulsion system. The latest update provided by ESA estimates that GOCE will stop ion propulsion around October 19 when the tank pressure drops below 2.5 bar.

October 8, 2013

Plot: Heavens-Above.com

As of October 8, 2013, GOCE was still orbiting in a stable orbit that the spacecraft is maintaining using its propulsion system. Re-Entry updates will be posted right here as soon as the vehicle runs of of Xenon and starts dropping in altitude.